In the field of nanomaterials, nanowires comprising semiconductors are commercially desirable and can be implemented across a broad variety of applications including electronics and optoelectronics. However, while growth of semiconductor nanowires in small quantities and/or as thin films is common, both large-scale synthesis and bulk growth continue to present significant challenges.
Conventional processes for synthesizing nanowires include the vapor-liquid-solid (VLS) approach and the solid-liquid-solid (SLS) approach. Traditionally, SLS and VLS have been applied on relatively large, monolithic substrates to yield two dimensional growth (see 100 in FIG. 1a). FIG. 1b contains illustrations depicting VLS and SLS applied to monolithic substrates. In VLS growth 101, the semiconductor material is supplied as a gas and is adsorbed by liquid nanodroplets of an appropriate catalytic material formed on a substrate. The nanodroplets serve as seeds for nanowire growth. The semiconductor material condenses at the interface between the droplet and the nanowire. The SLS process 102 is similar to VLS growth except that in SLS growth, the semiconductor material is supplied as a solid. The catalyst and the semiconductor material form a liquid mixture from which the semiconductor material condenses to form the semiconductor nanowire.
Traditionally, SLS and VLS have been applied on relatively large, monolithic substrates to yield two dimensional growth. When applying SLS or VLS to a monolithic substrate, nanowire synthesis is limited to growth directions away from the substrate. Furthermore, the nanowires being attached to the substrate conform to the surface 100 and do not fill the available volume. In one modification to the traditional approach, referring to FIG. 1a, the semiconductor material can comprise a powder, rather than a monolithic substrate, and the powder granules are coated with the catalyst. The use of the semiconductor powder can lead to three dimensional growth 104 that is easily scalable.
One common problem associated with SLS growth using semiconductor powders is that the composition of the nanowires resulting from SLS growth is inconsistent and hard to control. Furthermore, existing SLS and VLS approaches, whether implemented with powders or monolithic substrates, do not typically facilitate the synthesis of nanowires comprising multiple elements. Accordingly, a need exists for improved methods of synthesizing semiconductor nanowires.